Header row not appearing at the top of CSV while using Outputters - azure-data-lake

Question

In u-sql query dumping data from one csv file to another through Outputterss.Csv() function but header row with column names is appearing at the end of file instead of top.Please find my code below.Thanks for the help.
#telDataResult=
SELECT
"vin" AS vin,
"outsideTemperature" AS outsideTemperature,
"EventProcessedUtcTime" AS EventProcessedUtcTime,
"PartitionId" AS PartitionId,
"EventEnqueuedUtcTime" AS EventEnqueuedUtcTime,
"IoTHub" AS IoTHub
FROM #telData
UNION
SELECT
t.vin ,
Convert.ToString(outsideTemperature) AS outsideTemperature
EventProcessedUtcTime ,
PartitionId ,
EventEnqueuedUtcTime ,
IoTHub
FROM
#telData AS t
UNION
SELECT
t.vin ,
Convert.ToString(outsideTemperature) AS outsideTemperature
EventProcessedUtcTime ,
PartitionId ,
EventEnqueuedUtcTime ,
IoTHub
FROM
#telData1 AS t;
OUTPUT #telDataResult
TO
#"wasb://blobcontainer#blobstorage.blob.core.windows.net/cluster/logs/2016/outputofADLA.csv"
USING Outputters.Csv();

Answer 1

When you use a native outputter, the individual rows are written in a parallel fashion by multiple vertices, so there is no guarantee of order. We are currently working on supporting the output of header rows natively. In the meantime, you can use our custom outputter that writes header rows to output files. The custom outputter can be found in https://github.com/Azure/usql/tree/master/Examples/HeaderOutputter. Using the HeaderOutputter, your code will look like the following.
#telDataResult= SELECT
t.vin ,
Convert.ToString(outsideTemperature) AS outsideTemperature
EventProcessedUtcTime ,
PartitionId ,
EventEnqueuedUtcTime ,
IoTHub
FROM
#telData;
OUTPUT #telDataResult TO <OutputFile>
USING new new HeaderOutputter.HeaderOutputter(quoting:false);